Human
lung cancer that induced marked granulocytosis in both the patient and
tumor-transplanted nude mice (G2 mice) and from which
conditioned medium (G2-T-CM) exhibited human and mouse active colony-stimulating activity (CSA) has been reported (K. Ikeda et al.
Cancer Res 1985; 45:4144-4249). Recently, we found differentiation-inducing activity (
DIA) in G2-T-CM, which differentiated human promyelocytic leukemic cells (HL-60) to macrophage-like cells. Differentiated HL-60 cells were considered to be mature macrophages as judged by the positivity of
butyrate esterase activity, the acquisition of
Fc receptor, and the increment in capacity of phagocytosis and
nitroblue tetrazolium reduction. The
DIA in G2-T-CM was not attributed to
interferons known to have
DIA, because
interferon activity was not found in G2-T-CM by bioassay (less than 4 U/ml) and by radioimmunoassay for gamma-IFN (less than 0.1 U/ml). Molecular weight of
DIA was 36,000 Da and separated from CSA of which molecular weight was 22,000 Da by gel filtration on
Sephadex G-150.
DIA and CSA were also separated on chromatofocusing chromatography, because isoelectric point of
DIA was mainly less than 4.0 and that of CSA was 4.3-5.7. This
DIA was stable after heat treatment (56 degrees C for 30 min or 100 degrees C for 10 min) and in acidic condition (pH 2.0 for 24 hr). G2-T-CM is a good source of
differentiation-inducing factor for further purification and molecular cloning.